Circuit for electrical space discharge devices and method of operating same



AME

June 25, 1946. H. KLEMPERER CIRCUIT FOR ELECTRICAL SPACE DISCHARGE DEVICES AND METHOD OF OPERATING S Filed June 27, 1942 VOLTHGE 0R CURRENT //v VE/VTOR. fin/vsgfjnrskzk,

Patented June 25, 1946 CIRCUIT FOR ELECTRICAL SPACE DIS- CHARGE DEVICES AND METHOD OF OPER- ATING SAME Hans Klempcrer, Belmont, Mass, assignor to Itaytheon Manufacturing Company, Newton, Mass, a corporation of Delaware Application June 2'7, 1942, Serial No. 448,862

. 11 Claims.

. v 1 This invention relates to a method of operating, and to circuits for electrical space discharge devices having pool cathodes and igniting electrodes of the resistance-immersion type, such devices being generally known as ignitrons."

Ignitrons are adapted to be fired by pulses of electrical energy supplied to' their igniting electrodes. Each of these pulses of energy is adapted to produce an incipient are spot or spark, which becomes a self-supporting cathode spot when the discharge is established within the ignitron. The igniting electrodes referred to herein are constructed of a poorly conducting or semi-conducting material, for example, boron carbide or silicon carbide- This material is immersed in the oathode pool in intimate contact therein.

In some cases it is desirable to fire i nitrons with igniting impulses of comparatively short duration. such as for example of the order of two microseconds, or less, and having comparatively small energy content, such as for example, .1 watt second, or less. These igniting impulses may be derived from the discharge of a condenser. The wave form of a discharging condenser is not however the ideal form for such igniting impulses. Therefore, it is an object of the present invention to provide an ignition system employing igniting impulses having a short duration and low I energy content, which, at the same time, have a wave form more closely approximating the ideal type of form of igniting impulses.

Ignitrons are usually employed to control the flow of large currents. Frequently such ignitrons are operated at a high potential above ground. It has therefore'been necessary to insulate all parts of the circuit directly connected to the ignitrons. It has been the custom in practice to connect the ignition circuits for supplying igniting impulses to such ignitrons directly to the igniting electrodes and the cathodes thereof. It is another object of the present invention tozprovide means for separating. said ignition circuits from the load circuits of ignitrons.

In supplying igniting impulses to the i niting electrodes of ignitrons it has heretofore been necessary to use a comparatively large control device such as a comparatively large gaseous rectifying tube. Since the igniting current to be controlled by said gaseous rectifying tube has a peak value between 20 and 40 amperes, thetube employed is comparatively expensive. It is therefore a further object of this invention to provide ignition systems for ignitrons enabling the use of tubes with comparatively small cathodes and which are therefore comparatively inexpensive.

In supplying igniting impulses to ignitrons it is necessary that said igniting impulses be unidirectlonal. For this purpose it has been customary to utilize rectifying means in the ignition circuits.

A further object of the present invention is the provision of ignition circuits for ignitrons in which no rectifying means is required.

Still another object of the present invention is the provision of ignition circuits for ignitrons enabling the use of spark gaps as a means for controlling the supply of igniting impulses to said ignitrons.

'Other and further objects and advantages of the present invention will become apparent and the foregoing will be best understood from the following description of exemplifications thereof, reference being had to the drawing in which:

Fig. 1 is a set of curves to which reference is made in, explaining my'invention, said curves having a qualitative rather than a quantitative significance;

Fig. 2 is a schematic diagram of an system embodying my invention;

ignition Fig. 3 is a schematic diagram-of a welding circuit having an ignition system embodying a. modiiied form of my invention; and

Fig. 4 is a schematic diagram of an ignition system embodying another modified form of my invention.

Referring now to Fig. 1 in which power is plotted against time, a represents a pulse of electrical'energy having a duration of the order of two microseconds, the power of said pulse being of the order of one kilowatt, said power depending mainly upon the geometry of the ignitron to which said power is applied. The fiat-topped ,plied figure (1 represents a desirable value and wave form for a pulse of electrical energy to besupto the igniting electrode of an ignitron for i i in an are spot thereon. Igniting impulses such. as this are capable of reliably firing an ignition if they carry a suflicient current and last for a long enough time. A desirable source for such impulses is the discharge from a comparatively small condenser charged to a comparatively high voltage. said condenser being adapted to supply a pulse of energy having a duration of the order of two microseconds. Said pulses, however,

may be as long as 20 microseconds or less down to the minimum critical time required to produce an incipient are spot, which is about .2 microsecond, varying with the voltage employed, the geometry of the ignitron and the specific temperture at which it is operating. The condensers employed are preferably of small capacity. of

electrode 3 of ignitron I.

Fig. 1.

from about .02 to one microfarad. These condensers are preferably charged soas to have an energy content of the order of .01 watt second. Curve 1) of Fig. 1 represents the discharging energy of a condenser of the type hereinabove mentioned and charged to the value indicated. It will be seen that the amount of energy supplied by the discharge of this condenser is of greater value than that required according to a, a representing the preferred value and wave form. While the ignitingimpulses indicated by curve b will reliably produce an incipient are spot, it is evident that a substantial portion of the energy represented by curve I) is unnecessary and only serves to introduce undesirable heat into the igniting electrode. By providing a suitable inductive impedance in series with the discharging condenser thedischarging energy will take the wave form represented by curve in Fig. 1. Curve c approximates more closely the idealized form of a and therefore represents a more eflicient type of igniting impulse. It has been found that the impedance employed in series with the discharging condenser may be an air core coil having an inductance of the order of' 10- or 10- henries, and having a built-in resistance of approximately 20 ohms. Of course it will be understood that while the foregoing values apply in one specific embodiment, these may be varied to correspond to the characteristics of the particular ignitron em- I a pool cathode 2, an igniting electrode 3, and an .anode 4 is adapted to be supplied with igniting impulses by the discharge of a condenser 5. Con.- denser 5 may be charged from any suitable source of direct current and for this purpose may have its positive side connected to a terminal 8, and.

its negative side connected through a current limiting resistor I to another terminal 8. Terminals 66 are adapted to be connected to a suitable source of direct current supply such as a direct current generator, rectifier, battery or the like. Condenser 5 isadapted upon discharge thereof tosupply igniting impulses to the igniting The discharge of condenser 5 is controlled by any suitable means, such as for example, a controlled gaseous rectifyingtube 8. The negative side of condenser .5 is connected directly to the cathode of ignitron I, and the positive side of condenser 5 is connected in series with tube 8 and an impedance 9 to the igniting electrode 3 of ignitron I. Tube 8 has its anode I0 connected to the positive side of con-'- any suitable control circuit I2, such as is well known to those versed in the art, may be employed. The control circuit I2 is connected to the control grid I3 and the cathode II of tube 8, to thereby control the conduction of said tube. As has been explained hereinabove in connection with Fig. l, the discharge of the condenser directly'through an igniting electrode would produce a curve of the type illustrated by curve I) of In order to produce the more desirable wave form of curve 0, impedance 8 is provided. Impedance 9 may be an inductance having a value of 10- to 10*? henries and may have a built-in resistance of the order of 20 ohms. The ignition circuit illustrated in Fig. 2 is adapted to fire ignitron I. Said ignitron may be arranged in any suitable load circuit as will be readily understood by those versed in the art. Such a load circuit is described in Fig. 3 hereinafter.

Referring now to Fig. 3, a welding system is there illustrated utilizing a modified ignition circult. In Figs. 2 and 3, as well as in Fig. 4. like numerals. are applied to similar elements thereof which function in a similar manner. Referring now to Fig. 3, a condenser 5 is adapted to supply igniting impulses to the igniting electrode 3 of ignitron I. Ignitron I is adapted to control the discharge of the comparatively large condenser I4 into the primary I5 of a welding transformer I6 having its secondary I'I connected to a suitable welding. load I8. Condenser I4 is adapted to be charged from any suitable source of direct current and for this purpose has its negative side connected-to one terminal I9, and its positive side connected to another terminal 20, terminals I8 and 20 being in turn connected to said source of charging current. Condenser It has its positive side connected to one end of the primary winding l5 of the welding transformer, and has its negative side connected through ignitron I to the other side of said primary winding I5, cathode 2 of ignitron I being connected to the negative side of condenser I4, and anode 5 thereof being connected to one end of the primary I5.

In Fig. 3 ignitron I is adapted to be supplied with igniting impulses from the discharge of condenser 5. The discharge of condenser 5 is controlled by the controlled gaseous rectifying tube 8. In order, however, that the ignition circuit including condenser 5 shall be separated from the potentials in the load circuit of ignitron I,

an igniting transformer 2| is provided. The secondary 22 of igniting transformer 2| has one end thereof connected to the igniting electrode 3 of ignitron I, and the other end thereof connected to the cathode 2 of said ignitron. The primary 28 of igniting transformer 2|, which is adapted to be supplied with igniting energy by the discharge of condenser 5, has one end thereof con-' nected directly to the negative side of condenser 5, and the other end thereof connected through tube 8 to the positive side of condenser 5.

I'tfwill be seen that transformer 2| serves to separate the load circuit of ignitron'l from the ignition circuit. In addition, transformer 2| has several other functions. -The inductance associated with said transformer serves to change the wave form of the discharge of-condenser I2 so that instead of having the wave form of curve b of Fig. 1 a wave form approximating that of curve c of said figure is produced. In this embodiment the use of an air core coil therefore becomes unnecessary, the desired inductance and resistance being presented by the transformer. Igniting transformer 2| is a step-down transformer and preferably is of a high ratio, such as for example, from 10 to 1 through to to l. Igniting transformer 2| is preferably designed in relation to the other constants of the circuit so that the discharge of condenser 5 therethrough is critically damped. Because of the high ratio of said transformer the resistance across the secondary thereof, as reflected in its primary, is so great as to produce critical damping. Thus, the impulses supplied to the igniting electrode 8 are substantially unidirectional. Furthermore, by the use of such a high ratio step-down transformer the control means for discharging condenser 5, in this embodiment control tube 8, may be of small current carrying capacity, thereby permitting the use of a smaller and less expensive tube. For example, if-ignitron l is of the type requiring a pulse of current having a peak voltage of about 200 volts and a peak current value of about 20 amperes it would be necessary, according to the system of the prior art, to employ a control tube capable of carrying 20 amperes. Such a tube would be quite large and comparatively expensive. trated in Fig. 3 if the step-down igniting transformer has a ratio, for example of to 1, the tube required would only have to have a current carrying capacity of 2 amperes at a relatively higher voltage, such as for example, 2000 volts.

Since the voltage useddoes not materially afiect the size of the tube employed, the size of the tube being mainly dependent upon the current to be passed therethrough, a comparatively small tube may .be used. In one specific case, igniting condenser has a value of .075 microfarad'and is charged to a potential of 1000 volts; the igniting transformer has a step-down ratio of 10 to l and the tube employed has a peak current carrying capacity of 2.5 amperes.

Referring now to Fig. 4, the ignition system there illustrated differs from that in Fig. 3 in that a rotary spark gap is used to control the discharge of condenser 5 into the primary winding 23 of igniting transformer 2|. The rotary spark gap 24 is connected in the place occupied in Fig. 3 by the controlled gaseous rectifying tube 8, Spark gap 24 is driven by a suitable timing mechanism 25 so that condenser 5 is discharged at a predetermined frequency. In one system employing the rotary spark gap, condenser 5 had a value of .002 microfarad and was charged to a potential of 10,000 volts. In this instance igniting transformer 2| had a step-down ratio of 100 to 1. It will therefore be seen that the igniting impulses supplied to igniting electrode 3 of ignitron I had a peak value of approximately 100 volts and 20 amperes. Because the current passing through the spark gap was comparatively small, being substantially 100 times smaller than the current supplied to the igniting electrode, the spark gap did not deteriorate rapidly, but instead had a relatively long effective life, Furthermore, since the resistance in the discharge circuit of condenser 5 was equal to the resistance of the igniting electrode multiplied by the square of the transformer ratio, this resistance was large enough to suppress substantially any oscillation or inverse current tending to be supplied to the igniting elec- ,trode.

From the foregoing it will be seen that I have provided means for improving the wave form of igniting impulses derived from the discharge of a. condenser in such a manner that the least possible energy is needed to initiate an arc in an from the foregoing that I have provided an igni- In the ignition system illusascaeos electrode of the ignitrons. Still further, it will be seen that I have provided an ignition system for ignitrons enabling the use of smaller, simpler, and less costly equipment. scribed in specific terms embodiments of my in vention it will be apparent that changes may be made without departing from the teachings thereof. for controlling the discharge of the condenser. Changes-may be made in the constants hereinabove set forth which are solely by way of example. Various load circuits as well as various methods of charging the condensers may be employed. Therefore. since numerous modifications will readily be apparent to those versed in this art it is desired that the appended claims be given a broad interpretation commensurate with the scope of this invention within the art.

What is claimed is:

1. In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, means for supplying igniting impulses to said igniting electrode, said means including a condenser and an igniting transformer, said igniting transformer having a primary adapted to be supplied with pulses of current by the discharge of said condenser, the secondary of said igniting transformer being connected to the igniting electrode and adapted to supply igniting impulses thereto, said igniting transformer having a step-down ratio in the range of from 10 to 1 through 100 to 1.

2. In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, said means including a condenser having a capacity of l microfarad, or less, and an igniting transtion system for ignitrons in which the igniting impulses derived from the condenser are substantially critically damped so that no rectifying means is required to prevent the oscillation of said igniting impulses as applied to the igniting former, said igniting transformer having a primary adapted to be supplied with pulses of current by the discharge of said condenser, the secondary of said igniting transformer being connected to theigniting electrode and adapted to supply igniting impulses thereto, said igniting transformer having a step-down ratio in the range of from 10 to 1 through to 1.

3. In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, a condenser for supplying igniting impulses to said igniting electrode, and means for discharging said condenser through said igniting electrode, said means including an igniting transformer having a primary adapted to be supplied with pulses of igniting current by the discharge of said condenser, the secondary of said igniting transformer being connected to the igniting electrode and adapted to supply igniting impulses thereto, and means for controlling the discharge of said condenser into the primary of said transformer, said discharge controlling means including a rotary spark gap.

4. In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, a condenser for supplying igniting impulses to said igniting electrode, and means for discharging said condenser through said igniting electrode, said means including an igniting transformer havin a primary adapted to be supplied with pulses of igniting current by the discharge of said condenser. the secondary of said igniting transformer being connected to the igniting electrode and adapted to supply igniting impulses thereto, and means for controlling the discharge of said condenser into the primary of said transformer. said While I have de Other control means may be utilized 7 discharge controlling means including a rotary spark gap, said igniting transformer being designed in relation to the other constants of the system to produce critical damping of the discharge of said condenser.

5. In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, a condenser .for supplying igniting impulses to said ignitin electrode, and mean for discharging said condenser through said igniting electrode, said means including a step-down igniting transformer adapted to be supplied with pulses of igniting current by the discharge of said condenser, the

device having an anode, a pool cathode, and a' resistance-immersionigniting electrode, a condenser for supplying igniting impulses to said igniting electrode, and means for discharging said condenser through said igniting electrode, said means including an igniting transformer adapted to be supplied with pulses of igniting current by the discharge of said condenser, the secondary of said igniting transformer being connected to the igniting electrode and adapted to supply igniting impulses thereto, and means for controlling the discharge of said condenser into the primary-- of said transformer, said discharge controlling means including a rotary spark gap, said igniting transformer having a step-down ratio in the range of from 10 to 1 through 100 to 1 and being designedin relation to the other constants of the combination to produce critical damping of the discharge of said condenser.

7. In combination, an electrical space discharge 8. In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, means for supplying igniting impulses having a duration of from about .02 to 20 microseconds to said igniting electrode, said means including a. condenser, means for charging said condenser, a circuit for discharging said condenser through said igniting electrode, said circuit including an inductance arranged in series with said condenser.

9. In combinatioman electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, means for supplying igniting impulses having a. duration of from about .02 to 20 microseconds to said igniting electrode, said means including a condenser having a capacity of the order of range from .02 to l microfarad, means for charging said condenser, and a circuit for discharging said condenser through said igniting electrode, said aircuit including an inductance of from about 10'. to 10- henries arranged in series with said condenser. I

10. In combination, an electrical space dischargedevice having an anode, a pool cathode. and a resistance-immersion igniting electrode, means for supplying igniting impulses having a duration of the order of two microseconds to said igniting electrode, said means including a. condevice having an anode, a pool cathode, and a resistance-immersion igniting electrode, means for supplying igniting impulses having a duration of the order of two microseconds to said igniting electrode, said means including a. condenser. means for charging said condenser, and a critically damped circuit for discharging said condenser through said igniting electrode.

denser, means for charging said condenser, an igniting transformer havinga primary adapted to be supplied with pulses of current by the discharge of said condenser and having a secondary connected to the igniting electrode.

11. In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, means for supplying igniting impulses having a duration of the order of two microseconds to said igniting electrode, said means including a condenser having a capacity of the order of range from .02 to 1 microfarad, said circuit including an inductance of from about 1(i to 10- henries arranged in series with said condenser, and an igniting transformer having a primary adapted to be supplied with pulses of current by the discharge of said condenser and having a secondary connected to the igniting electrode, said igniting transformer having a step-down ratio of the order of range between 10 to 1 and to l.

Hans mmnana. 

